Why not add more elsif branches to your sub? You say you're worried about bmul behaving badly if it's handed something other than a BigInt, so why not just check for it?

You could also run some tests or read the source to find out what bmul really does if the 2nd operand isn't a BigInt.

Why would you have to explicitly bless your integers if you made a subclass of Math::BigInt?

And to step back a little: are you sure you want to do overloading? Will future users (or yourself) be flummoxed that $a*$b isn't doing what they expect? Is typing '$obj->mult($other_thing)' really that bad? At least that way you know exactly what you just did.

Well, I had a look at Math::BigInt source code and it seemed to me that the '*' overloading had already a lot of elsif branches. I just don't want to reinvent the wheel and redo what has already been done. Basically I whish I could just say "if the second operand is a My::Custom::Object then do this, otherwise just do whatever '*' does in the Math::BigInt class".

About explicit blessing, I just don't see how I could do it otherwise, unless I use a constructor anyway. But now that you make me think of it , I wonder if the magic of bigint wouldn't be inherited. I have to check this out, indeed.

You are right about using overloading not being necessary. But it would definitely be cool.